1. Field of the Invention
Despite the ancient character of the growth of single cells, particularly yeast in fermentation and more recently unicellular organisms in the production of antibiotics, there have been few significant advances in the design of reactors for the use of single cells in commercial processes. In growing cells efficiently to produce a product which is to be isolated, a large number of considerations are involved.
For high efficiency, it is desirable that there be a high cell density so that a substantial proportion of the volume of the reactor is filled with closely packed viable cells. In order to obtain high densities, it is necessary to have efficient distribution of nutrients, so that substantially all of the cells are bathed in a growth supporting nutrient medium. Both economics and cell viability put a limit on the amount of nutrients that can be introduced into the nutrient medium. Furthermore, product will frequently inhibit cell production of the product. Therefore, an efficient means must be provided for continuously removing product to maintain a concentration level of the product below a predetermined level. In addition, cells are fragile and can easily be broken. Dead cells remaining in the reactor reduce the efficiency of the reactor by occupying space which could otherwise be occupied by viable cells.
A further consideration is obtaining the product cell free. That is, if the product containing medium exiting the reactor includes cells, these cells must be removed. Employing microfilters creates numerous problems in slowing down the flow of the liquid, becoming clogged by cells, and adding significant capital costs and processing costs.
It is therefore desirable to provide new and improved reactors for growing single cells, particularly microorganisms, such as bacteria and yeast, to provide for economic and efficient production of microbiological products.
2. Description of the Prior Art
U.S. Pat. No. 3,580,840 describes the method and apparatus using microorganisms for sewage treatment employing a porous membrane. U.S. Pat. No. 3,767,790 teaches microorganism entrapment for controlled release. See also U.S. Pat. No. 3,860,490. U.S. Pat. No. 3,875,008 teaches microorganism encapsulation in a hollow filament. U.S. Pat. No. 4,148,689 teaches entrapment of microorganism in a gelled sol.